1. Field
The invention concerns generally the technology of spacecraft propulsion. Specifically the invention concerns the technology of using electrical power to produce thrust by displacing the geomagnetic field in the vicinity of a spacecraft.
2. Prior Art
Spacecraft currently require rocket engines to maneuver while in orbit and to change their orbit. When a satellite has used up all its propellant, its orbit gradually changes until the satellite can no longer be used for its intended purpose. For this reason it is customary to de-orbit a satellite before its propellant has been completely expended; regardless of the health of its electronic systems. If a spacecraft propulsion system that does not use an expendable propellant could be developed the cost of doing business in space would be greatly reduced.
Electric propulsion is considered for tasks where low to moderate thrust for an extended period of time is required. Electrical power can be continuously generated on spacecraft with solar panels or nuclear reactors. It would be advantageous to be able to use this power to produce thrust for a spacecraft after it has achieved orbit.
Field propulsion is a propellantless spacecraft propulsion system that uses electrical power and derives its thrust by acting against the Earth's magnetic field. This type of propulsion is also referred to as electrodynamic propulsion. The geomagnetic field is non-uniform in the vicinity of the poles and a few other locations. A Magnetic Sail takes the form of a large area current-carrying loop, or multiple loops of wire; preferably a Superconductor. If a large current passes through this loop in the vicinity of a non-uniform magnetic field, thrust is created. This source of propulsion is known from the prior art of J. F Engelberger “Space Propulsion System” U.S. Pat. No. 3,504,868. Related prior art is “Electromagnetic Ground to Orbit Propulsion Method and Operating System for High Mass Payloads”, U.S. Pat. No. 5,093,313.
Throughout most of the Earth's orbital space the geomagnetic field is essentially uniform. A current loop will generate a torque within a uniform field. There are two general methods in the prior art for generating a unidirectional force within a uniform magnetic field. Electrodynamic tethers have their origins in a paper by Drell, Foley, and Ruderman “Drag and Propulsion of Large Satellites in the Ionosphere: An Alfven Propulsion Engine in Space”.
Failure Resistant Multiline Tether, U.S. Pat. No. 6,260,807, proposes the use of a very long conductive tether to push against the geomagnetic field in order to create thrust. It is essentially a long conductor that is oriented at right angles to the geomagnetic field, electrically connecting two regions of the ionosphere. A current passes through it, transferring charge between the two regions of the ionosphere. Another method for generating thrust with a tether uses an on board power supply to send current through the tether. In this application the return path for the current is provided by the charged particles surrounding the tether. Electrodynamic tethers have the capability of generating large thrusts, but are difficult to deploy because of their long length.
Spinning Electrodynamic Tethers, U.S. Pat. No. 6,942,186, address some of the tether deployment problems but would require rocket engines to achieve the deployment and to keep the spinning tether in an orientation that would allow it to push against the geomagnetic field.
Combination solar sail and electrodynamic tether propulsion system, U.S. Pat. No. 6,565,044, proposes the use of a solar sail in outer space and a conductive tether to push against the geomagnetic field while in earth orbit to create thrust. This has the same deployment problems as an Electrodynamic Tether and the added difficulties of deploying a solar sail.
In the United States Statutory Invention Registration US004001605, “Supercurrent Bifilar Twister”, Leupold discloses methods whereby superconductors can trap magnetic flux and then displace or bend it, thereby changing the potential energy. A bifilar helix formed from superconducting wire is disclosed and its use in the generation of a helical magnetic field is presented.
In the US Patent Application 2009/0314269 “Helical Field Accelerator”, Victor et at disclose a magnetic pressure accelerator with helical magnetic structures disposed concentrically that are driven in opposite directions, for the purpose of accelerating a magnetic projectile contained within the interior of the device.
Another method for generating a unidirectional force with a uniform magnetic field is known from the prior art of R. J. R. Ladouceur, Major RCAF “Shielded Coil Electrodynamic Propulsion (SCEP) A Feasibility Study” (1993). This thesis studies the feasibility of using high permeable magnetic shields to isolate sections of a single or multi-turn current loop from an external field. The torque is not completely eliminated with this method.
Another method for SCEP proposes the use of Superconductors for shielding, exploiting the Meissner effect or other properties of Superconductors. Magnetic Floatation Device, patent application 2008/0111655, presents a coaxial Superconductor device. The theory of this device is that if an inner conductor is the return path for a persistent current on the outside the device, only the magnetic field resulting from the outside currents would act on the Earth's geomagnetic field. The conclusion of this theory is that a force vector, which could be utilized as upward thrust, would be generated.